Reach stackers are vehicles with rubber tires, fitted with a diesel engine and an operator's cabin, similar to a retracted mobile crane. They can transport and stack containers. The previously known reach stackers are designed with a container spreader fixedly connected to the telescopic arm, i.e. the spreader raising movement is only carried out via the telescopic arm. In known reach stackers, the operator's cabin is arranged fixedly or movably connected on the frame in the rear part on the vehicle, which always permits a good view for the operator of the container spreader fixedly connected to the telescopic arm with the current design.
It is advantageous with reach stackers to make the rear wheels as steered wheels. The steering system for the steering of the wheels includes a steering wheel and a mechanical link between the steering wheel and the steering linkage associated with the steered wheels of the rear axle. To permit a simple steering for the driver of the reach stacker, which is heavy in part, in particular under load, electronically supported steering systems are already known, that is steering systems in which the steering movement is supported via servo motors in accordance with the steer angle. Nevertheless, conventional steering systems in reach stackers, which are guided from the operator's cabin to the steered rear wheels, are complex and costly in construction.
It is one object of the present application to provide a steering system for telescopic loaders, in particular reach stackers, which is simple in construction and easy to operate.
In one embodiment, this object is satisfied in accordance with a telescopic loader, in particular a reach stacker, which has a steering command input device, at least one pick-up to sense the steering angle and a processor unit which is in communication with the steering command input device and with the at least one pick-up and which generates a pre-set signal which can be forwarded to a steering actuator.
In one example, the telescopic loader or reach stacker has a so-called “steer-by-wire” steering system. In this steering system, the steering movement of a steering command input device is electronically transmitted from the steering command input device to the steering linkage in that the nominal steering angle value pre-set by the operator is initially transmitted to an electronic control system “by wire”. The electronic control system then transmits the adjustment command “by wire” to an actuator or to a steering actuator which can be made as a hydraulic servomotor or as an electric servomotor and generates the steering movement at the steering linkage. The electronic control system processes signals from different sensors. The two most important signals are the nominal value for the steering angle, which is pre-set by the operator at the steering command input device, and the actual value of the position of the steering linkage at the steered rear wheels, which results from the adjustment movement of the actuator.
Further features can provide additional advantages. For example, the steering command input device can advantageously be a joystick. Generally, different “electronic” steering wheels such as a rotating disk or similar would also be feasible as a steering command input device.
The processor unit can particularly advantageously have means by means of which an optimum steering speed can be determined in dependence on one or more operating parameters which can be sensed. Operating parameters of this kind can, for example, be the vehicle speed or the vehicle yaw rate.
It is particularly advantageous with a telescopic loader, in particular a reach stacker, compared with a conventional mechanical steering system, that the steering ratio can be selected freely, for example as a function of the vehicle speed. The steering force support provided can also be freely programmed. In this way, it may be possible to vary the steering ratio and steering force with changes in operating conditions. An active dynamic steering angle correction, which serves the increase of the driving stability, could also be provided as an additional function.